The present invention relates generally to apparatus and methods for detecting arc faults, and more specifically to arc fault detection apparatus and methods that are less susceptible to nuisance tripping.
Arc fault detection apparatus and methods are known that employ a micro-controller to measure voltages associated with a load, and to process data representing the voltage measurements to determine the presence of electrical arcing. For example, a conventional arc fault detection apparatus may be configured to sense an alternating load current, to filter and rectify the AC signal, and to provide the rectified signal to an integrating capacitor. The conventional arc fault detection apparatus may then use a micro-controller to take measurements of the voltage across the integrating capacitor, and to convert the voltage measurements to digital data for subsequent processing using an algorithm. For example, such an algorithm may be employed to analyze the measured voltage levels corresponding to respective cycles of the line voltage, and to determine whether the voltage measurements are characteristic of an electrical arc fault such as point contact, low level, or series electrical arcing, or a nuisance load such as a dimmer control, a motor, incandescent lighting, appliance thermostat switching, drill current transitions, random line voltage spikes, EMI bursts, etc. In the event the voltage measurements are characteristic of an arc fault, the conventional arc fault detection apparatus typically trips a circuit breaker to disconnect the power output from the load.
Although the above-described conventional arc fault detection apparatus can be employed to detect and distinguish between electrical arc faults and nuisance loads, there is a need for arc fault detection techniques that have increased reliability. For example, electrical arcing indicative of an arc fault is generally chaotic in nature. In contrast, nuisance loads such as triac-controlled dimmer circuits can produce electrical arcing events that are periodic. However, conventional arc fault detection apparatus often cannot reliably distinguish between periodic and non-periodic electrical arcing events, and are therefore prone to nuisance tripping. Further, nuisance loads such as dimmer controls, motors, and incandescent lighting can generate high voltage transients as the settings of these devices are changed, thereby producing decreasing or increasing levels of electrical arcing over consecutive time periods. However, conventional arc fault detection apparatus frequently have difficulty distinguishing between electrical arc faults and electrical arcing events characterized by a transient decrease or increase in voltage levels, which are generally indicative of a nuisance load. In addition, although some loads may produce noisy switching signals having abnormally high voltage levels, such high voltage levels are not necessarily indicative of electrical arcing and may be incorrectly characterized as arc faults by conventional arc fault detection apparatus.
It would therefore be desirable to have improved arc fault detection apparatus and methods that avoid the drawbacks of the above-described conventional arc fault detection apparatus and methods.